The present invention concerns an implant device for correcting an abnormal condition known as flat foot (Talipes planus), and particularly an expanding implant device to reshape the natural arch of a foot having that condition.
In order to remedy this condition in a child, which is due to the loss of normal anatomic connections of the talus and the calcaneus, it has recently been suggested to introduce a prosthetic device into the subtalar tunnel between the talus and the calcaneus. However, this introduction of such a prosthetic material presents the problem of maintaining the material in the subtalar tunnel, which anatomically has the form of a funnel which opens laterally, i.e., toward the outside. Thus, it is known to implant a screw to provide a temporary talus-calcaneus gliding joint restoring to the various parts their normal anatomical relationships and which brings into play the restructuring action associated with the growth of the child. The growth erases the dysplasia and restores the cohesion of the whole. Maintenance is achieved by a trans-talus-calcaneus screw and once the restructuring is achieved, the temporary attachment is removed, freeing the subtalus pair.
Around 1975 it was proposed to utilize a silicone prosthesis having a generally frustoconic form and which has an appendage. The overall arrangement is very close in form to a wine glass. Its geometry permits it to be very congruent with the space in which it must be implanted. Thus, its form permits this prosthesis to be perfectly adapted in that space.
The drawbacks of such a prosthesis are linked on the one hand to the silicon material whose behavior in response to mechanical forces is not completely known and on the other hand to the associated surgical technique. In effect, in order to introduce this implant, the physician must make a double incision, one on the medial face and the other on the lateral face of the foot.
In order to eliminate these drawbacks, there has been created another device whose implantation requires only a single incision. This endo-orthesis is made of a high density polyethylene and has the form of a cylinder having a rim at its base. It has a funnel-shaped opening along its longitudinal axis and a screw is introduced into this opening. The cylinder is cut over the interior 2/3 of its length into four quarters intended to be expanded under the effect of the advance of the screw along the axis of the cylinder. The endo-orthesis is threaded interiorly. This device has for its function to open the subtalar tunnel in order to reposition the talus relative to the calcaneus. The major drawback of this implant is that its expanded form is not absolutely congruent with the subtalar tunnel cavity, even after insertion of the internal screw into the axial passage.